We need tp try to find out...Sure the intake charge will be a little slower, in particular at low RPMs. At higher engine speed and with load there will be another port providing more intake charge. How bad can that be? Also if you could stage the throttle you might be able to achieve higher velocity with the primaries alone at low RPMs. I just hate to build this complicated intake manifold and have it not work.

CW

 

also semi-PP is complicated from the view of injection split.
we could estimately calculate difference in size between different ports but size is not the only total air flow devider. speed and port configuration also matters.
how much in % of the total injection do we need to route to each port?
incorrect split might lead to poor air/fuel mixture and many troubles.

 

Don't see a problem there. IF it was we have it now, just with the stock set-up. People keep changing injector sizes all the time. I ran only primary injectors to a certain RPM and boost pressure with no problems. Once the fuel is suspended in the air it will mix fine with just air from another port. Don't forget it will all end up in the same combustion chamber. You could argue that if you spray your secondaries to early where there is little charge velocity in the larger secondary ports that your fuel atomisation will be poor and you waste a lot of fuel for no performance. That will be even worth with a larger PP port. Luckly the secondary injectors are mounted further away from the combustion chamber giving the fuel a better chance to mix properly with the air and I would mount the injector for the PP as far back as I can.

 

well , i played a little on the dyno with my street ported 20b and noticed that changing injection ratio between primary and secondary ports reflects in AFR change and HP change.
I tried to change values from 55/45 to 65/35 and finished at 62/38.
i have my injection advance and phase tables configured well in the ECU thus i think that is the only matter of the mixing quality. With semi-PP this might be much more significant.

 

That is interesting, I didn't think it would make a significant difference. So keeping fuel the same you tune the split until you saw the richest AF an then tuned the fuel again? What injector set-up do you have?

 

yes, like that. my setup is 6x1600cc via peak&hold driver.

 

Holy crap...that is a lot of fuel you can push

 

yeah,i reached 85% duty with it at 11.7 AFR should be around 900-1000HP.
my new setup is 15x1600cc on a new custom short 3 rotor engine but i will run it on alcohol.

 

Well, yes and no. I'm new here BTW, but I am currently working on PP with primaries on my motor. From the research I've done, this setup is far more streetable than a full PP with all side ports filled. The reason is because you can modify the LIM to accomodate the PP, thus leaving the primaries in place to better control idle. The guy who did this setup in Japan, car idles very well, and he has all the flow benifits of a PP. There's a couple of pics on this setup and when I find them I will post. Good luck.

 

so much of that is going to depend on how quick the turbo spools.

assuming engines of equal hp, the faster spooler wins.

 

Well my plan is to do this NA, I'll be using a spreadbore Holley(primaries to primaries and large secondaries to P-Port) I should be able to control the fuel ration via primary and secondary jets. I am keeping the primaries with straight runners and individual tubes. The secondaries however, will have an open plenum. The goal is somewhere around 300 to the wheels.